linux-kernel - Re: [PATCHv2 2/2] iommu/arm-smmu-qcom: Move the adreno smmu specific impl earlier

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Date:   Fri, 26 Feb 2021 10:23:28 -0800
From:   Rob Clark <robdclark@...il.com>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>,
        Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        Jordan Crouse <jcrouse@...eaurora.org>,
        Akhil P Oommen <akhilpo@...eaurora.org>,
        "list@....net:IOMMU DRIVERS <iommu@...ts.linux-foundation.org>, Joerg
        Roedel <joro@...tes.org>," <iommu@...ts.linux-foundation.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>
Subject: Re: [PATCHv2 2/2] iommu/arm-smmu-qcom: Move the adreno smmu specific
 impl earlier

On Fri, Feb 26, 2021 at 9:24 AM Bjorn Andersson
<bjorn.andersson@...aro.org> wrote:
>
> On Fri 26 Feb 03:55 CST 2021, Sai Prakash Ranjan wrote:
>
> > Adreno(GPU) SMMU and APSS(Application Processor SubSystem) SMMU
> > both implement "arm,mmu-500" in some QTI SoCs and to run through
> > adreno smmu specific implementation such as enabling split pagetables
> > support, we need to match the "qcom,adreno-smmu" compatible first
> > before apss smmu or else we will be running apps smmu implementation
> > for adreno smmu and the additional features for adreno smmu is never
> > set. For ex: we have "qcom,sc7280-smmu-500" compatible for both apps
> > and adreno smmu implementing "arm,mmu-500", so the adreno smmu
> > implementation is never reached because the current sequence checks
> > for apps smmu compatible(qcom,sc7280-smmu-500) first and runs that
> > specific impl and we never reach adreno smmu specific implementation.
> >
>
> So you're saying that you have a single SMMU instance that's compatible
> with both an entry in qcom_smmu_impl_of_match[] and "qcom,adreno-smmu"?
>
> Per your proposed change we will pick the adreno ops _only_ for this
> component, essentially disabling the non-Adreno quirks selected by the
> qcom impl. As such keeping the non-adreno compatible in the
> qcom_smmu_impl_init[] seems to only serve to obfuscate the situation.
>
> Don't we somehow need the combined set of quirks? (At least if we're
> running this with a standard UEFI based boot flow?)
>

are you thinking of the apps-smmu handover of display context bank?
That shouldn't change, the only thing that changes is that gpu-smmu
becomes an mmu-500, whereas previously only apps-smmu was..

BR,
-R